Some custom primary key tests (added at #17631, #17696, #18220, #18228)
were lost at #26266. Restore the tests to improve test coverage.

The PR #27384 changed migration compatibility behaviour.

```ruby
class CreateMasterData < ActiveRecord::Migration[5.0]
  def change
    create_table :master_data, id: :integer do |t|
      t.string :name
    end
  end
end

```

Previously this migration created non-autoincremental primary key
expected. But after the PR, the primary key changed to autoincremental,
it is unexpected.

This change restores the behaviour of the compatibility layer.

The PR #27384 changed integer-like primary key to be autoincrement
unless an explicit default. This means that integer-like primary key is
restored as autoincrement unless dumping the default nil explicitly.
We should dump integer-like primary key with default nil correctly.

Fix typo in guide: _articles should be _article

The guide contains a typo in the "local_assigns" section, where
rendering a model named 'Article' via `render @articles` is shown to
render a partial called `_articles.html.erb`, when in fact the necessary
partial name is `_article.html.erb`

Fix collection_singular_ids= bug

Fix a test of AR::Type::TypeMap#lookup when using Oracle

Ignore yarn error log file

When the association's primary key is manually set as a symbol and called with an array of strings, CollectionAssociation#ids_writer
fails to cast the ids to integers. This is because
AssociationReflection#association_primary_key_type and
ThroughReflection#association_primary_key_type return the incorrect
type, since ModelSchema.type_for_attribute only accepts a string. The
result is an ActiveRecord::RecordNotFound error.

generate mailer layout files only when it does not exist

Fix CI failure caused by aa647b46

sub_template_message distracts Rails.root from its message only when Rails.root is defined,
and Rails.root is defined at tools/test.rb

since the test names become Regexp filters, non-escaped test names cause RegexpError on isolated test via bin/test

This causes TypeError when loaded separately

If already have layout files, in many cases use it.

According to the commit comment on 54d84cbb, AJ/bin/test was intentionally not added,
but AJ tests doesn't actually do anything special other than specifying ENV['AJ_ADAPTER'],
which can be easily done via command line environment variable.

MySQL generated columns: https://dev.mysql.com/doc/refman/5.7/en/create-table-generated-columns.html
MariaDB virtual columns: https://mariadb.com/kb/en/mariadb/virtual-computed-columns/

Declare virtual columns with `t.virtual name, type: …, as: "expression"`.
Pass `stored: true` to persist the generated value (false by default).

Example:

    create_table :generated_columns do |t|
      t.string  :name
      t.virtual :upper_name, type: :string,  as: "UPPER(name)"
      t.virtual :name_length, type: :integer, as: "LENGTH(name)", stored: true
      t.index :name_length  # May be indexed, too!
    end

Closes #22589

Currently, executing the `test_initialize_raises_an_ArgumentError_if_no_block_given`
test alone will result in an error.

```
$ ./bin/test test/evented_file_update_checker_test.rb -n test_initialize_raises_an_ArgumentError_if_no_block_given
Run options: -n test_initialize_raises_an_ArgumentError_if_no_block_given --seed 6692

# Running:

E

Error:
EventedFileUpdateCheckerTest#test_initialize_raises_an_ArgumentError_if_no_block_given:
NameError: uninitialized constant EventedFileUpdateCheckerTest::Listen
    rails/activesupport/test/evented_file_update_checker_test.rb:21:in `teardown'
```

This is because if do not specify a file or directory for
`EventedFileUpdateChecker`, do not require `listen`, and using listen
method in teardown.
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/evented_file_update_checker.rb#L53..L65

Therefore, added listen's require to avoid errors.

call `gem` `erubis` before require

For inform that need to add `erubis` to gemfile.

Currently, executing the `test_initialize_raises_an_ArgumentError_if_no_block_given`
test alone will result in an error.

```
$ ./bin/test test/evented_file_update_checker_test.rb -n test_initialize_raises_an_ArgumentError_if_no_block_given
Run options: -n test_initialize_raises_an_ArgumentError_if_no_block_given --seed 6692

# Running:

E

Error:
EventedFileUpdateCheckerTest#test_initialize_raises_an_ArgumentError_if_no_block_given:
NameError: uninitialized constant EventedFileUpdateCheckerTest::Listen
    rails/activesupport/test/evented_file_update_checker_test.rb:21:in `teardown'
```

This is because if do not specify a file or directory for
`EventedFileUpdateChecker`, do not require `listen`, and using listen
method in teardown.
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/evented_file_update_checker.rb#L53..L65

Therefore, added listen's require to avoid errors.

remove unused variable

This removes the following warnings.

```
activesupport/test/file_update_checker_shared_tests.rb:279: warning: assigned but unused variable - checker
```

Fix missing partial iteration

Chain scope constraints should respect own table alias

The `ActiveJob::TestHelper` replace the adapter to test adapter in
`before_setup`. It gets the target class using the `descendants`, but if
the test target job class is not loaded, will not be a replacement of
the adapter.
Therefore, instead of replacing with `before_setup`, modified to
replace when setting adapter.

Fixes #26360

Fixes #27666.

Use temporary connection pool for sqlite3_mem adapter

Feature/active job test helper

Fix inherit from deprecated `ActionView::Template::Handlers::Erubis`

Get neglected TODO done in render_test

Freeze default empty string for sql_type in get_oid_type

Fixes #27826
Refer https://github.com/rails/rails/commit/f7b317175430a2d9300d9c4acfc1f34f4fdb2fbc

There are some classes inherit from `ActionView::Template::Handlers::Erubis`.
(ex. https://github.com/haml/haml/blob/4.0.7/lib/haml/helpers/safe_erubis_template.rb#L3)

```
Class.new(ActionView::Template::Handlers::Erubis)
# => TypeError: superclass must be a Class (ActiveSupport::Deprecation::DeprecatedConstantProxy given)
```